In a known general traveling hydraulic working machine, a hydraulic pump is of the fixed displacement type, and the maximum absorption torque of the pump is also constant (fixed). Therefore, a proportion at which the engine output torque is distributed between respective operations of the hydraulic pump and travel (transmission) is constant and so is a maximum torque for the travel.
In connection with such a known general traveling hydraulic working machine, Japanese Patent No. 2968558 proposes an improved one employing a variable displacement hydraulic pump in such a manner that the maximum absorption torque of the hydraulic pump can be changed. According to this related art, the sum of respective loads of a travel driving device and a working actuator (i.e., the sum of the absorption torque of the hydraulic pump and the transmission torque (travel torque)) is detected. When the load sum is smaller than the output torque of an engine, the maximum absorption torque of the variable displacement hydraulic pump for the working actuator is maintained at a setting value, and when the load sum becomes larger than the engine output torque, e.g., when the machine is in a combined stall state, the maximum absorption torque of the variable displacement hydraulic pump is reduced, while the travel torque is increased to obtain a large tractive force. As a result, the engine output can be effectively utilized.
Patent Reference 1: Japanese Patent No. 2968558